Screening apatites for (U-Th)/He thermochronometry via continuous ramped heating: He age components and implications for age dispersion

Well-behaved examples such as the Durango standard and other apatites with good age reproducibility show the expected smooth, sigmoidal gas-release curves predicted for volume diffusion using typical apatite kinetics, with complete exhaustion by ∼900 °C for linear heating at 20 °C/min. Secondary factors such as U and Th zoning and alpha-loss distribution have a relatively minor impact on such profiles. In contrast, samples having greater age dispersion show significant He release in the form of outgassing spikes and He release deferred to higher temperatures. Screening results for a range of samples permit us to assess the degree to which CRH screening can identify misbehaving grains, give insight into the source of extraneous He, and suggest that in some cases it may be possible to correct ages for the presence of such components.